1. Field of the Invention
The invention relates to a detecting device. More particularly, the invention relates to a disposable capillary electrophoresis detecting device where a capillary electrophoresis (CE) microchip and an electrochemical sensor microchip are integrated.
2. Description of Related Art
Capillary electrophoresis has been applied in the field of clinical medicine, food sanitation, and environmental inspection. To be specific, the clinical applications of CE mainly aim to detect neurotransmitters or molecular bioinformatics in blood or cerebrospinal fluid; as to the field pertinent to food sanitation, CE is often applied to detect pesticide residue, illegal additives, and other poisonous residues; in terms of environmental inspection, the CE technique is frequently employed to detect presence of heavy metals or environmental hormones. In general, the detecting method to which the CE technique may be applied includes an optical detecting method and an electrochemical detecting method. Since the optical detecting method requires large-sized detecting equipment and cannot be performed in a rapid manner in response to the requirement for on-the-spot inspection, the CE detecting method integrated with the electrochemical detecting method has been prevailing recently.
The high separation efficiency of the CE technique is mostly achieved by interaction between electrophoretic and electroosmotic flow (EOF) for separating the ions/molecules with positive charges, negative charges, or no charges. Due to the recent development of the lab-on-a-chip (LOC) technology, the CE capillaries may also be miniaturized on a portable microchip. Besides, the detecting method may also be adjusted in compliance with the requirement of the electrochemical sensor microchip, so as to miniaturize the entire microchip and simplify the entire detecting process.
According to the relative positions of the electrochemical electrode and the capillary channel, the electrochemical sensors integrated with the CE microchip may be categorized into the following three types: (1) the in-channel type: the working electrode is placed in the separation channel and in the separation high-voltage electric field; (2) the off-channel type: the working electrode is placed in the separation channel, and a decoupler is applied to shunt the separation high-voltage electric field, thereby eliminating the disturbance of the separation electric field to the detecting electrode; (3) the end-channel type: the working electrode is placed on the outside of the separation channel and around the outlet of the CE capillaries, either on or off chip. In the on-chip alignment mode of the end-channel detection, the electrode and the capillary separation channel are incorporated into the same substrate of the microchip; in the off-chip alignment mode, the electrode and the capillary separation channel are formed on different substrate of the microchips. In case of the in-channel detection, the off-channel detection, and the on-chip mode of the end-channel detection, the electrode and the capillary separation channel are formed together; accordingly, if it is necessary to modify the electrode, change the material of the electrode, or replace the damaged or polluted electrode, the electrode cannot be replaced individually, which leads to repetitive manufacturing and increases manufacturing costs. By contrast, the off-chip mode of the end-channel detection requires that the electrode and the capillary separation channel are formed separately and then assembled together, thus facilitating the fabrication and reducing the manufacturing costs.
Nonetheless, the integration of the off-chip type of the electrochemical sensors and the CE microchip is subject to the difficulty in aligning the outlet of the capillary of the CE microchip to the detecting electrode, and thus the off-chip type mode has not been prevalent. To be specific, the electrochemical detecting tank is far greater than the width of the CE capillary, which lessens the pushing force of the EOF; at this time, the bands of sample which are originally concentrated will be swiftly dispersed. If the outlet of the CE capillary is not aligned to the electrochemical detecting electrode, and if the distance between the outlet and the electrochemical detecting electrode is not properly monitored, the sensitivity and reproducibility of the detection will be deteriorated. A number of methods have been proposed to adjust the distance between the outlet of the CE capillary and the electrochemical detecting electrode, whereas most of these methods rely on the use of an optical microscope or a micro-positioning device. This inevitably raises the complexity of replacing the detecting electrode and also fails to comply with the real-time requirement for the on-the-spot inspection.